The present invention relates to a microwave oven, and more particularly to an automatic cooking control method capable of cooking a food with a low moisture content at an optimum by utilizing a variation in output voltage of a humidity sensor.
FIG. 1 is a block diagram of a typical microwave oven.
As shown in FIG. 1, the microwave oven includes a key input unit 1 for inputting given data, a sensor control unit 2 for sensing the moisture content of a food and transmitting it, and a central processing unit 3 for receiving output signals from the key input unit 1 and the sensor control unit 2 and controlling various units of the microwave oven in accordance with the received signals. The microwave oven further includes a high-frequency oscillating drive unit 4 for heating the food under a control of the central processing unit 3, a display unit 5 for displaying digital information on the current cooking conditions of digital, and a fan motor drive unit 6.
FIG. 2 is a flowchart illustrating a conventional automatic cooking control method applied to the microwave oven of FIG. 1.
As shown in FIG. 2, in accordance with this method an initialization is performed after application of power (step S2). Thereafter, a determination is made about whether a humidity sensor (not shown) has reached its self heat-emitting state (step S3). When the humidity sensor has reached its self heat-emitting state, a zero-balancing is carried out for making the humidity sensor meet an initial state of the microwave oven (step S6).
However, when the humidity sensor has not reached its self heat-emitting state yet, a determination is made about whether one minute has elapsed (step S4). Where one minute has lapsed, the operation is determined as an error (step S5). When one minute has not elapsed yet, the operation returns to the step S3.
After the zero-balancing performed at the step S6, a heating is initiated by a heater equipped in the humidity sensor (step S7). Then, the minimum voltage Vmin is determined by reading an output value from the humidity sensor every second (step S8).
Thereafter, a determination is made whether the output voltage from the humidity sensor has reached a sensing voltage Vs corresponding to the previously determined data value applied from the key input unit 1 (step S9). Where the output voltage has reached the sensing voltage Vs, as shown in FIG. 3, an additional heating time KT.sub.1 is calculated by multiplying the time T.sub.1 taken until the output voltage reaches the sensing voltage Vs by an intrinsic constant K determined depending on the food (step S12). Additional heating is then performed for the calculated additional heating time KT.sub.1 (step S13). At step S14, the cooking is completed.
When it is determined at the step S9 that the output voltage from the humidity sensor has not reached the sensing voltage Vs yet, a determination is made about whether the time T.sub.1 taken in reaching the sensing voltage Vs has exceeded 20 minutes (step S10). If 20 minutes has elapsed, the cooking is completed but the operation is determined as an error (step S11). If not, the operation returns to the step S9.
At the step S9, the sensing voltage Vs is determined to be Vmin+.DELTA.V. Vmin represents the minimum voltage determined at the step S8 and .DELTA.V represents a minute voltage varied depending on the kind of the food and stored in a memory (not shown) equipped in the central processing unit 3. Therefore, the sensing voltage Vs is a voltage varied depending on the food.
As the sensing voltage Vs varies, the time T.sub.1 is varied. Such a variation in time T.sub.1 results in a variation in cooking time.
The intrinsic constant K is obtained from the memory of the central processing unit 3 which stores intrinsic constants of various foods.
As apparent from the above description, the conventional method used for automatically cooking a food with a high moisture content senses a vapor generated when the food is cooked, thereby sensing the kind of the food and determines the sensing voltage Vs appropriate for the sensed food kind. Then, this method performs a heating for the time T.sub.1 taken in reaching the sensing voltage Vs and then an additional heating for the time KT.sub.1 determined by multiplying the time T.sub.1 by the intrinsic constant K determined depending on the kind of the food.
In this method, there is no problem in cooking a food with a high moisture content, because the cooking is performed in accordance with a data value determined from the sensed moisture. In case of a food, such as bacon or popcorn, having a low moisture content to be cooked in a short time, a slight variation in cooking time results in a difficulty to achieve the optimum cooking, because the time T.sub.1 taken in reaching the sensing voltage Vs is varied. For instance, where popcorn is cooked in accordance with the conventional automatic cooking control method, the popcorn may be half-done or burned.